The trial of Charles Taylor - the former president of Liberia and the first former African leader to face an international court - opens in The Hague today where he is accused of war crimes during the diamond-fuelled conflict in neighbouring Sierra Leone.

Human rights groups have welcomed the trial at a special court of international and Sierra Leonean judges as an important erosion of the climate of impunity that has encouraged atrocities in some of Africa's most brutal wars.

The prosecutor will open the trial, which is expected to last for a year, by detailing 11 war crimes charges against Mr Taylor. He is accused of forming a "joint criminal enterprise" by giving Sierra Leonean rebel groups weapons and training in return for access to the country's diamond fields. It alleges that Mr Taylor was complicit in the Revolutionary United Front rebel group's campaign against civilians, which included mutilation, usually the chopping off of arms or hands, and the abduction of women and girls as sex slaves and men and boys as soldiers. Many were held for years.

Mr Taylor, who ruled Liberia from 1997 to 2003, has pleaded not guilty, saying he has immunity because he was a head of state at the time of the alleged crimes. But at an earlier hearing, the court invoked the precedents of the Nuremberg and Tokyo war crimes trials, and the tribunals for Rwanda and the former Yugoslavia, to rule that immunity does not extend to crimes against humanity. Mr Taylor faces up to life in prison if convicted. Britain has offered to jail him.

The former Liberian president will not be called to account by the special court for the long list of crimes he is alleged to have committed in his own country during an equally brutal 14-year civil war. Even so, Human Rights Watch, one of several groups that pressed for many years for Mr Taylor to be brought to justice, said the trial showed that leaders responsible for war crimes could be called to account.

"To see someone [tried] of the standing of Charles Taylor, who has been associated with abuses throughout west Africa, is really significant," said Elise Keppler, legal counsel for the group's international justice programme.

The court was jointly established by the Sierra Leonean government and the UN after a security council resolution in 2000. Mr Taylor was indicted in 2003, but he sought refuge in Nigeria - which eventually agreed to extradite him. Mr Taylor fled and was captured near Nigeria's border with Cameroon.

He is being held at the Hague for fear that a trial in Sierra Leone could destabilise the country. It is not his first stint in prison: in 1984, he was jailed in the US on an extradition warrant for allegedly embezzling $922,000 from the Liberian government. He escaped from a Massachusetts prison by sawing through a bar of his cell and sliding down a knotted sheet.

He resurfaced in Libya, establishing a relationship with Muammar Gadafy that proved fateful for Liberia and Sierra Leone. Mr Taylor also met the future RUF leader, Foday Sankoh, at a military training camp in Libya. After Mr Sankoh launched his insurgency in 1991, he turned to Mr Taylor and Mr Gadafy for support, offering diamonds in exchange for weapons. Although diamonds are not mined in Liberia, under Mr Taylor the country became a major diamond exporter.

Human rights groups also want Mr Taylor held to account for crimes in Liberia after his rebellion against the president, Samuel Doe, in 1989. Mr Doe was tortured to death by one of Mr Taylor's allies, Prince Johnson. A video of the killing sold well in west Africa. But Mr Johnson split with Mr Taylor soon afterwards and seized control of the capital, Monrovia, prompting a long civil war underpinned by ethnic divisions; Mr Taylor went on to exploit practices of ritual killings in Liberia to sow terror in his 14 year war for power.